Phenyloxiranecarboxylic acid esters, for example 2-phenyloxirane-2-carboxylic acid ethyl ester, inter alia, are within the scope of an investigation into the ability of substituted cyclic compounds (with a three-membered ring) to serve as a substrate or inhibitor for epoxide hydrase from guinea pig liver microsomes [F. Oesch et al., Biochem. 10 (1971) No. 26, 4,858-66]. Reaction of methyl N-acetyl isatoate with an excess of diazomethane yielded methyl 2-(o-acetamidobenzyl)glycidate in the course of the elucidation of the constitution of isamic acid [P. de Mayo and J. J. Ryan, Can.J.Chem. 45 (1967) 2177-2190]. Certain substituted oxiranecarboxylic acids have now been found to be pharmaceutically-active compounds with a specific action.